Holography is a technique which enables three-dimensional images (holograms) to be made which involves the use of a laser, interference, diffraction, light intensity recording and suitable illumination of the recording. The image changes as the position and orientation of the viewing system changes in exactly the same way as if the object were still present, thus making the image appear three-dimensional.The holographic recording itself is not an image; it consists of an apparently random structure of either varying intensity, density or profile.
The Hungarian-British physicist Dennis Gabor was awarded the Nobel Prize in Physics in 1971 for his invention and development of the holographic method. His work done in the late 1940s, built on Extraordinary work in the field of X-ray and microscopy by other scientists including Mieczysław Wolfke in 1920 and WL Bragg in 1939. The discovery was an unexpected result of research into improving electron microscopes at the British Thomson-Houston Company in Rugby,England,and the company filed a patent in December 1947.The technique as originally invented is still used in electron microscopy, where it is known as electron holography, but optical holography did not really advance until the development of the laser in 1960.
The development of the laser enabled the first practical optical holograms that recorded 3D objects to be made in 1962 by Yuri Denisyuk in the Soviet Union and by Emmett Leith and Juris Upatnieks at the University of Michigan, USA.Early holograms used silver halide photographic emulsions as the recording medium. They were not very efficient as the produced grating absorbed much of the incident light. Various methods of converting the variation in transmission to a variation in refractive index known as “bleaching” were developed which enabled much more efficient holograms to be produced.
Holography is a technique that enables a light field which is generally the product of a light source scattered off objects which to be recorded and later reconstructed when the original light field is no longer present, due to the absence of the original objects.Holography can be thought of as somewhat similar to sound recording, whereby a sound field created by vibrating matter like musical instruments or vocal cords and is encoded in such a way that it can be reproduced later, without the presence of the original vibrating matter.
Holograms are recorded using a flash of light that illuminates a scene and then imprints on a recording medium, much in the way a photograph is recorded. In addition to that part of the light beam must be shone directly onto the recording medium – and this second light beam is known as the reference beam. A hologram requires a laser as the sole light source. Lasers can be precisely controlled and have a fixed wavelength, unlike sunlight or light from other conventional sources, which contain many different wavelengths. To prevent external light from interfering, holograms are usually taken in darkness,or in low level light of a different color from the laser light used in making the hologram. Holography requires a specific exposure time (just like photography), which can be controlled using a shutter,or by electronically timing the laser.